Multilayer piezoelectric ceramic electronic components, such as multilayer piezoelectric actuators, offering a great displacement even at low voltage have been in growing demand in recent years.
The production of a piezoelectric ceramic electronic component of this type usually involves alternately stacking piezoelectric ceramic layers and conductive layers for use as inner electrodes and cofiring the resulting stack.
It is desirable that the inner electrodes be made of Ni, a material available at relatively low prices.
Ni is easily oxidized when fired in an air atmosphere and needs to be fired in a reducing atmosphere. A piezoelectric material is therefore required that can be cofired in a reducing atmosphere.
Firing a PZT- or PT-based material, which contains Pb, in a reducing atmosphere, however, does not result in desired piezoelectricity because Pb is reduced. Furthermore, Pb is an environmental stressor and its use is unfavorable to the environment.
From this perspective, Patent Document 1 proposes a piezoelectric ceramic composition that contains a main ingredient represented by a general formula {(1−x)(K1-a-bNaaLib)(Nb1-cTac)O3-xM2M4O3} (where M2 represents at least one of Ca, Ba, and Sr, M4 represents at least one of Zr, Sn, and Hf, and x, a, b, and c meet the following conditions: 0.005≤x≤0.1, 0≤a≤0.9, 0≤b≤0.1, 0≤a+b≤0.9, and 0≤c≤0.3) and 2 to 15 moles of Mn per 100 moles of the main ingredient, with the M4 content in the range of 0.1 to 5.0 moles per 100 moles of the main ingredient.
In this Patent Document 1, a non-lead alkali niobate compound as the main ingredient is mixed with some particular elements including Mn to the above formulation in order to make the compound more suitable for sintering in a reducing atmosphere, with the intention to prevent incomplete sintering and attain good piezoelectricity even when cofiring the composition with a Ni-based inner electrode material in a reducing atmosphere.
Patent Document 1: International Publication No. 2008/152851 (e.g., Claim 1)